The present invention relates to marine dye compositions. Marine dye compositions have been used in a number of applications to mark the location of crashed aircraft, life rafts and military equipment, for example rockets.
Life preservers used in aircraft in particular have been provided with a fluorescein dye placed in a cotton bag. The bag was sufficiently porous to allow water to seep through and dissolve the fluorescein dye. The disadvantages associated with using this system are as follows:
1. The bag could be easily ripped and the dye lost prematurely.
2. Once sufficient water had been absorbed by the bag and it became detached, it could float below the surface of the water.
3. The dye often caked due to moisture being absorbed by the bag from the air. Furthermore the rate of diffusion of the dye through the cotton bag could not be controlled.
The specification of U.S. Pat. No. 3,263,012 discloses a composition which purports to overcome these problems. The composition disclosed comprises a fluorescein compound bound in a matrix of polyvinyl alcohol resin containing glycerine and borax. The composition is pressed into a cake and made into a relatively thin plate like object. The principal object of the invention disclosed in this U.S. patent is to supply a composition that provides a controlled release of dye into water over an extended period of time, for example up to 45 days. The purpose of the glycerine is said to be to swell the polyvinyl alcohol resin and to dissolve the dye thereby permitting the dye to diffuse into the resin and to be encapsulated in the resin matrix. In addition, the specification states that the glycerine partially controls the rate of diffusion of the dye from the polyvinyl alcohol matrix into the water when the device is ejected into the sea. The more glycerine the greater the rate of emission of dye into the water. The presence of borax appears to be for the purpose of maintaining the cohesive strength of the resin matrix.